Cathodoluminescence (CL) features of the Anatolian agates, hydrothermally deposited in different volcanic hosts from Turkey

Two different types of multi-colored gem-quality agate samples were investigated. They are both found in the same area in the Çubuk-Ankara region of Turkey although the first group is morphologically and geologically distinct from the second, being nodular-shaped agates occurring in cavity-spaces of a rhyolite host rock with an acidic character. They generally do not have any macroscopic inclusions, but the second group of rather block-shaped agates occurs in the fracture-spaces of an andesite host rock with a more neutral character, i.e. of lower free silica content, and they may display pseudomorphic bar-like macroscopic inclusions.Cathodoluminescence results at room temperature were obtained using measurements with alternating current (AC) (at energies of 14 and 24 keV) as well as direct current (DC) (at 14 keV energy), and they display remarkably different patterns between the two types of agates. It reveals a relation between the CL emissions and the presence of some transition metal elements. It is obvious that all trace elements do not play a direct role.Gaussian fitting of the cathodoluminescence AC experimental data at 14 keV energy obtained from the agates of rhyolite host indicates that there are three major spectral emissions, the dominant one being in the longer-visible wavelength region (red region) at about 690 nm. Additionally, two lesser emission lines occur in the middle-visible wavelength region (yellow region) at about 590 nm, and in the smaller-visible wavelength region (blue region) at about 430 nm. In spite of these, the same data from the agates of andesite host indicate that there is only one remarkable spectral emission which is in the in the middle-visible wavelength region (yellow region) at about 590 nm.On the other hand, Gaussian fitting of the cathodoluminescence AC experimental data at 24 keV energy obtained from the agates of rhyolite host indicates that these initial spectral emissions shift from the red and yellow regions to the orange and green regions respectively, even though the emission in the blue region is nearly constant. In spite of these, Gaussian fitting of the cathodoluminescence AC experimental data at 24 keV energy obtained from the agates of andesite host indicates that the initial spectral emission shifts from the yellow region to the green region, but also that a new minor emission develops in the blue region at about 430 nm. It is interpreted that these changes represent a maturation reaction in the microcrystalline quartz structure consisting of a condensation reaction eliminating water between neighboring paired silanol (Si-OH) groups to develop a strained Si-O-Si bond.     

Defect detection in semiconductor layers with built-in electric field with the use of cathodoluminescence

Cathodoluminescence (CL) in scanning electron microscopy (SEM) is commonly accepted as revealing local properties of a specimen region illuminated by an electron beam. CL is widely used to visualize defects in semiconductor structures. However, the presence of a strong electric field in, for example, heterojunctions or p–n junctions causes a separation of generated electron–hole (e–h) pairs and suppresses recombination in the specimen region excited by the beam. As a result CL – a radiative recombination – becomes quenched. At the same time, electron beam-induced current (EBIC) flows throughout the structure, which may produce secondary electroluminescence that is registered by the CL detector. Consequently, the CL measurement is distorted and if there are defects in the structure, they remain unrevealed. The current study shows that registration of the CL signal for different values of electron beam current (including high ones) enables true defect detection in semiconductor layers with built-in electric field. Results for a special test structure prepared with focused ion beam on AlGaAs/GaAs laser heterostructures with an 8 nm InGaAs quantum well are presented.     

The origin of yellow band emission and cathodoluminescence of Au-catalyzed wurtzite GaN nanowires

GaN nanowires with large yield are directly synthesized by simply ammoniating the gallium oxide powders in the presence of ammonia gas at 1000 °C, under the assistance of Au nanocatalysts. The microstructure and crystallinity of as-synthesized GaN nanowires are well studied by using high-resolution transmission electron microscope (HRTEM) and some structural defects such as stacking faults are found in the GaN nano-crystal. Cathodoluminescence measurement shows that a strong near-band-edge (NBE) emission band centered at 384 nm and a broad yellow band in the range of 500–800 nm are observed. Finally, the growth mechanism and possible optical emission process of GaN nanowires are discussed.     

Studies of minority carrier transport in ZnO

The temperature dependence of the minority carrier diffusion length and lifetime in bulk n-type ZnO was studied using Electron-Beam-Induced Current (EBIC) and cathodoluminescence (CL) techniques. The diffusion length was observed to increase exponentially over the temperature range from 25 to 125 C, yielding an activation energy of 45 ± 2 meV. A concomitant decrease of the cathodoluminescence intensity for the near-band-edge transition was also observed. The activation energy determined by optical measurements was 58 ± 7 meV. The larger minority carrier diffusion length and smaller luminescence intensity are attributed to the increased lifetime of non-equilibrium holes in the valence band at elevated temperatures. Carrier trapping on Li-related levels with activation energy 283 ± 9 meV is also addressed.     

Cathode luminescence characteristics of ZnGa2O4 phosphor thin films with the doped activator

The zincgallate (ZnGa₂O₄) phosphor thin film was grown using RF magnetron sputtering system at various process parameters. A ZnGa₂O₄ phosphor thin film was deposited on Si(1 0 0) substrate and annealed by a rapid thermal processor (RTP). The X-ray diffractometer (XRD) patterns indicate that the Mn-doped ZnGa₂O₄ phosphor thin film shows a (3 1 1) main peak and a spinel phase. A ZnGa₂O₄ phosphor thin film has better crystallization due to increased substrate, annealing temperature and deposition time. Also the ZnGa₂O₄:Mn phosphor thin film shows green emission (510 nm, ⁴T₁→⁶A₁), and the ZnGa₂O₄:Cr phosphor thin film shows red emission (705 nm, ⁴A₂→⁴T₂).     

UV cathodoluminescence of crystalline α-quartz at low temperatures

Two luminescence bands in the UV range were detected in crystalline α-quartz under electron beam excitation (6 kV, 3-5 μA). One band is situated at 5 eV and could be observed in pure samples. Its intensity increases with cooling below 100 K and undergoes saturation below 40 K alongside a slow growth with the time of irradiation at 9 K. The decay curve of the band at 5 eV contains two components, a fast (<10 ns) and a slow one in the range of 200 μs. The photoluminescence band at 5 eV with a similar temperature dependence was found in previously neutron-irradiated crystalline α-quartz. Therefore, the band at 5 eV was attributed to host material defects in both irradiation cases. The creation mechanism of such defects by electrons, the energy of which is lower than the threshold for a knock-out mechanism of defect creation, is discussed. Another band at 6 eV, containing subbands in different samples, appears in the samples containing aluminum, lithium and sodium ions. This luminescence is ascribed to a tunnel radiative transition in an association of (alkali atom)⁰-[AlO₄]⁺ that is formed after the trapping of an electron and a hole by Li⁺ (or Na⁺) and AlO₄.     

Blue and infrared cathodoluminescence induced by carbon-irradiation in SrTiO3 single crystal

We show that blue-CL can be induced in SrTiO₃ single crystal at room temperature by irradiating it with 60 KeV carbon ion (C⁻) beam. An infrared CL-emission is induced simultaneously. Transmission electron microscopy (TEM) measurement exhibits an 200 nm thick surface layer formed by the C⁻ irradiation. We show that the emitting region can be patterned into any desired shape by fabricating the STO surface using Pt-based micro-lithography technique.     

Met.(Cu,Ag)-TCNQ有机薄膜的EB CL像

自从1979年Potember等人首先发现了CuTCNQ有机薄膜具有受电流控制的电开关特性以来[1]，有关CuTCNQ及AgTCNQ这些阴离子基过渡金属盐（以下简称为Met．（CU、Ag）-TCNQ）有机薄膜的光存储特性、光电开关特性，以及某些气教特性的研究结果便不断报导出来[2-4]，引起人们极大的兴趣．作为很有前途的有机光电功能材料，至今对其电导及光电特性的机理研究仍显得十分薄弱，极大影响了它们进一步向实用器件方向的发展．由于CuTCNQ的晶体参数至今未见报导，我们依据CuTCNQ粉末X射线小角衍射谱对比AgTCNQ相应的粉末X射线衍射数据，…     

Highly efficient cathodoluminescence of nanophosphors by solvothermal route

The low voltage excited nano-size of SrTiO₃: Pr, Al red cathodoluminescent phosphors is successfully prepared by hydrothermal and solvothermal processes. Crystal size does not have obvious growth after post-annealing process under the nucleation seeds control. The nanophosphors synthesized by the solvothermal process have a more stoichiometric and cubic SrTiO₃ structure than the hydrothermal ones. SrTiO₃: Pr, Al nanophosphors synthesized by the solvothermal process with 200 °C/24 h possess a cubic crystal size of about 50 nm. The red cathodoluminescent intensity of 200 °C/24 h-solvothermal phosphors is nine times that of the 250 °C/24 h-hydrothermal ones after 1000 °C/1 h heat treatment. The stoichiometric SrTiO₃: Pr, Al nanophosphors by solvothermal preparation need less amounts of Pr activator and Al dopant than when using conventional solid-oxide preparation and can achieve high cathodoluminescence at a wavelength of 615 nm exciting at a low accelerating voltage of 1 kV. The solvothermal process combined with the post-annealing process to synthesize nanophosphors distributes and excites the activator and the dopant more homogeneously and efficiently in the host structure of SrTiO₃, thus enhancing luminescence.     

Optical and structural characterization of a self-aligned single electron transitor structure by cathodoluminescence microscopy

We report about optical and structural investigations of a self-aligned single electron transistor (SET) structure using cathodoluminescence-(CL) and transmission electron microscopy (TEM). The SET structures were fabricated by MBE growth of GaAs/AlAs on different prepatterned GaAs (1 0 0) substrates. This technique for the in situ formation of nanoscopic semiconductor heterostructures is presently a widely used and promising approach for the fabrication of low-dimensional systems like quantum wires and quantum dots (QD). The active region of the SET structure consists of a GaAs/AlGaAs-QD formed by thickness modulation of a single quantum well (SQW) during the MBE growth. The position and the size of the QD is defined by the design of the substrate pattern. The thickness modulation of the GaAs-SQW is evidenced by TEM investigations. The lateral confinement potential given by the thickness modulation of GaAs-SQW is directly imaged by CL microscopy.